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Karoo thorn

Karoo thorn

Black locust

Honey locust branched thorns

Honey locust leaves & pods

Dagger wattle

Hedge wattle1

Hedge wattle2

family

Fabaceae, subfamily Mimosoidae (wattles)

status

Karoo thorn (Vachellia karroo, formerly Acacia karroo) is listed as noxious in class 1 (a notifiable weed which must be eliminated if found) throughout NSW. It cannot be propagated and sold. It is an African species which has been planted in a few locations in southern Australia. These trees have been removed and soil contaminated with seed has been quarantined to prevent infestations developing. Another infestation in Western Australia has also been destroyed. Karoo thorn is on the federal government alert list of 28 environmental weeds which currently have a limited Australian distribution but show considerable weed potential. The complete eradication of these species from Australia is highly desirable.

Description

Karoo thorn is a fast-growing shrub or tree to 25m high. It has conspicuous long spines several cm long, which are in V-shaped pairs. Leaves are bipinnate (feathery), green and hairless. Flowers are yellow and similar to native wattles (Acacia species). Seed pods are flat and hairless. The photo of this weed was provided by Peter Martin (CRC for Australian Weed Management).

Preferred habitat and impacts

Its adaptation to the dry African savannah climate and its rapid growth make this species potentially very invasive in Australia and the long spines make it unpleasant to deal with. It could greatly reduce carrying capacity in pastoral land, make mustering difficult, provide harbour for feral animals and seriously affect biodiversity.

Dispersal

Long-lived seed could be dispersed in contaminated soil.

Look-alikes

Mesquite (Prosopis species) are similar. They also have bipinnate leaves, wattle-like yellow flower clusters (long rod-shaped ones, not ball-shaped) and paired or single thorns 4-60mm long at the base of each leaf. They are also declared noxious in class 2 in Southern Slopes and Upper Lachlan LCAs, and because they are in a notifiable class (1, 2 or 5), cannot be propagated or sold anywhere in NSW. See the entry for this weed for more information on it.

The environmental weeds black locust (Robinia pseudoacacia) and honey locust (Gleditsia triacanthos) are similar in having pinnate (once-divided) or bipinnate foliage, thorns or long spines at the base of each leaf (and sometimes scattered on the trunk) and flat pea or bean-like pods. The flowers of black locust are pea-like, not wattle-like, and held in long drooping clusters of many cream to yellow flowers. The thorns are small, curved and paired. Honey locust flowers are inconspicuous, while its thorns are long and branched on the trunk, with two smaller thorns at each leaf base. There are thornless varieties.

There are some wattles (Acacia species) native to the South Coast and Southern Tablelands which either have sharply pointed leaves or prickles on the stems. Two are illustrated, hedge wattle (Acacia paradoxa), which grows on the tablelands and slopes with an isolated population around Batemans Bay, and dagger wattle (Acacia siculiformis). Both have flowers and seed pods similar to karoo thorn, but lack the very long paired, white spines.

Control

Notify your local Council Noxious Weeds staff if you think you have seen this plant.